At low temperatures, polarization and increase of internal resistance easily happen in a battery, which causes a poor discharge capacity of a battery pack at low temperatures. In addition, at low temperatures, when charging, Li precipitation reaction easily happens, which causes decrease of battery safety performance. Therefore, it is necessary to heat the battery pack at low temperatures.
In the related art, the battery pack is generally heated by an external heating device. For example, a heating film is adhered to an outer surface of the battery or the battery pack, heat generated by the heating film is conducted to the battery or the battery pack; or a water-cycling system is installed in the battery pack, water in the water-cycling system is heated, so as to heat the battery pack.
In the two above-described heating manners, the battery or the battery pack is heated in a heat conduction way, and a heating rate is low, which results in a great difference between internal temperature and external temperature of the battery after being heated.